I have been keeping my eye on this thread since I bought my SR5004 in Jan 2010. I have not had any issues with this unit until tonight (Jan 22, 1011). Brief overview of my setup. Rogers SA 4250HD STB, connected via HDMI to Marantz SR5004. HDMI output of Marantz connected to Samsung 40" LCD.
I was watching TV, tuned in to Hi-Def so Dolby Digital was the audio mode. The video feed from the game I was watching was having issues and was pixelizing, along with this the audio was cutting in and out. I left the room just for a moment and heard what was more like a crackle then a pop, but the receiver turned off and the Standby light started blinking, indicating the "protect mode" that others have experienced.
I first tried unplugging the unit and plugging it back in, this did not work. Then I unplugged the unit while tracking down this forum again for the reset instructions. Plugged the unit back in after 5 mins, still the Standby light was blinking "Protect". I did the reset sequence, press and hold "Surr. Mode" + "Exit" + "Clear". Lucky for me after three seconds there were a few clicks from the relays in the unit and it powered back on without me losing any settings.
Based on what I saw and what the Cable STB was doing I would deduce that the fact the audio and sound streams were not pure could have caused issues in the decoder logic inside the unit and after it got "confused" enough it decided to just give up and put itself into protect. Hopefully this may assist Marantz in troubleshooting the problem, it seems to me as though it doesn't have the tolerance to deal with a "not-so-clean" audio signal.
Oh, BTW, S/N for my unit is MZ02094600XXXX